knutj@idt.unit.no (Knut Johannessen) (06/30/91)
I am employed by an organization turning from proprietary systems into the world of UNIX and TCP/IP. One task is a nationwide multiprotocol network. And therein lies a problem... We have been allocated several class B addresses. The available addresses may be allocated in three main ways: - divide the country into regions and allocate one class B address to each region (several minor variations possible) - allocate all the class B addresses throughout the country in a layered fashion. This proposal has serious drawbacks using the IGRP routing protocol. - allocate one class B address to a backbone network and use a remaining class B addresses as regional addresses (similar to the the first proposal) The entire network is preferably seen as a single network, hence the IGRP (and later OSPF) is the preferred routing protocol. The topology is similar to (not complete) ----A1--- / \ / \ / \ A2 E2 | | | | | | B1--------------D | / \ | / \ | / \ B2 / \ \ | | \ | | C1--------C2------E1 Each letter indicated one class B address, e.g. nodes A1 and A2 is within the same class B address-space. The allocation is hence following the first proposal with regions. Each node is implemented with one or more cisco AGS+. Not shown is the local networks connected to each node. Each line indicates a physical transmission resource. The main problem is efficient use of the available paths in the event of failure. E.g. with the proposed address allocation and the use of IGRP (and OSPF?) it will not be possible to route traffic from A1 to A2 following the paths A1-E2-D-B1-A2 as traffic from one class B address-space cannot be routed to a station within the same address-space via a different class B address. Similar problems exist e.g. with traffic from C1 to C2. The physical paths cannot be changed. One proposal, assuming regional allocation, is the use of secondary addresses. I.e. addresses from the A space is used at node E2, D and B1 to allow traffic from A1 to A2 to follow A1-E2-D-B1-A2. Hence, each regional network is "stretched" into the other regions - the result is not much different from the layered proposal. Any comments on - address allocation - use of secondary addresses (impact on efficiency?) - choice of routing protocol will be much appreciated. Knut ==== knutj@idt.unit.no ta@odin.nta.no